My SO Said We Would have to Break up If I Pursue my Career

I am [20M] dating my my long time friend of 5 years. We've been dating for a year almost and we both do music and well as we live together. I had a Convo with them about me wanting to open a music studio and my business ventures with music. They said that due to anxiety of cheating they couldn't date me at that point. They said it was due to not knowing what other peoples intentions around me are. They said they wouldn't want to get in the way of my career by stressing over it. I said it feels like an ultimatum but they said it's not bc they want me to pursue my career but they can't be a part of it. I asked if it was a situation of we would be friends and then date again when I settle down on my music goals and they basically said no bc we would be moving on to different chapters of our life. They also said they are replaceable which weirded me out. Also we are in a strong friend group of 4 so it would be really awkward to break up over that to me at least. I guess I understand but not really bc I trust perfectly regardless of if we are around each other. But I respect their mental health so we kinda ended the conversation. Now I don't know what to do. I'm not mad just disappointed and I don't know if I should feel hurt by this. I consider them to be a crucial part of life due to the fact they we have been there for each through so much. More than my family whom I don't even have a connection to anymore. They have also help me beat my drug addiction and depression. Kinda just at a loss honestly. Feeling extreme levels of apathy about it. Its just another coupled onto the fact that I'm ace so there is already tension in our sex life. Any advice would do me wonders.